Retarders are commonly used in railway classification yards, wherein railcars are caused to accelerate down a raised profile or hump towards a particular destination. As the railcars accelerate down the hump, the retarder applies braking pressure on the wheels of the railcar to prevent accidents or derailment and yet maintain a predetermined speed of travel of the railcar. Many different types of electro-hydraulic, air and mechanical retarders are known in the art, some examples of which are disclosed in U.S. Pat. Nos. 4,393,960 and 7,140,698, the disclosures of which are incorporated herein by reference.
Known air retarders are generally more robust and efficient than electro-hydraulic retarders. However railyard operators that already employ electro-hydraulic retarders have found the prospect of changing over to an air retarder system to be cost-prohibitive, especially because of the significant capital investment necessary to install an air plant. Also, these operators do not want to lose the significant amount of capital investment already made in equipment associated with the electro-hydraulic retarders, for example the battery back-up necessary to power the hydraulic retarders for a short period of time in the event of a power outage.
The applicant has therefore recognized that there is currently a significant need in the art for more efficient and effective electro-hydraulic retarder systems and methods of operating such systems.
Current electro-hydraulic retarders contain multiple sets of levers and brake shoes. A hydraulic piston cylinder activates an elaborate mechanical linkage to translate and rotate the levers to close the brake shoes to a width that is narrower than the width of the railcar wheel. When the wheel enters the retarder, the retarder must be capable of allowing the brake shoes to spread apart to the width of the wheel and yet still maintain the desired pressure on the side of the wheel; and the retarder must also allow for quick application and removal of pressure on the sides of the wheel. However because hydraulic system fluids are generally incompressible, it is currently difficult to use hydraulics to power a set of brake shoes in such a way that the brake shoes will quickly spread apart to accept an entering wheel and conform to the various widths of railcar wheels while maintaining a consistent pressure on the side of the wheel.
In addition, current electro-hydraulic retarders have many metal-on-metal wear surfaces and complicated linkage systems that require regular maintenance. These retarders do not meet life expectations and are difficult to repair.